Projects

Bassett Creek Main Stem Lagoon Dredging Project

Golden Valley and Minneapolis

Project Number: BC-7

Project Status | Complete

After a detailed feasibility study, in May 2020 the BCWMC approved implementation of the project to dredge all 3 lagoons to a depth of 6 feet (Alternative 2-all). A public hearing was held September 17, 2020; there was no public input received at the hearing and the project was officially ordered by resolution. The project was implemented (designed and constructed) by the BCWMC in close coordination with the Minneapolis Park and Recreation Board. Project design at the 50% phase were approved in December 2021. 90% designs were approved in June 2022. Construction began in early January 2023 and dredging was completed in March. Site restoration was completed in spring/summer 2023. A final report and recommendations for future dredging projects was presented in December 2023.

Project Funding | Grant Funded

The total cost of this project was estimated at $2,759,000 including feasibility study, design, construction, landfill disposal of contaminated sediment, and administration. However, final project costs are expected to be approximately $1,600,000 due to lower than expected engineering and construction costs.

Clean Water Grant Funding of $250,000 from the MN Board of Water and Soil Resources was awarded in late 2020. A $74,000 Hennepin County Opportunity Grant was awarded in 2021.The remaining project funds were collected through ad valorem property taxes collected over 2021, 2022, and 2023 by Hennepin County on property within the Bassett Creek Watershed.

Project Description

This project removed sediment that collected in three of the seven “lagoons” created along the Main Stem of Bassett Creek in Wirth Park, between Golden Valley Road and Highway 55. These lagoons were originally created in the mid-1930s by Civilian Conservation Corps crews. A 2015 study found that the lagoons remained relatively unchanged until the early 1990s, when large amounts of sediment began to appear in the lagoons. The sedimentation appeared to slow or stop by the mid-1990s. The sedimentation in Lagoon “E” (immediately to the east of the chalet and parking area) was of concern to City of Minneapolis and Minneapolis Park and Recreation Board (MPRB) staff because the sedimentation may be contributing to flooding of the parking lot and a short section of Theodore Wirth Parkway. The sedimentation resulted in the creation of new “islands” in the creek/lagoons that reduced the flow capacity and floodplain storage of the creek.

The project was originally designed to remove almost 40,000 cubic yards of accumulated sediment by excavating the lagoons to a 6-foot depth. However, the project actually resulted in only the removal of 25,650 cubic yards and a depth of less than 4 feet. Still, the project resulted in a reduction of approximately 390 pounds of total phosphorus and 101,000 pounds of total suspended solids per year that previously flowed downstream in the creek and into the Mississippi River. The cost benefit analysis of the completed project calculates a cost of $210/pound of total phosphorus/year removed. Due to high levels of toxic substances in the sediment, all dredged material required landfill disposal.

Additional project benefits include improved flow capacity and floodplain storage, and improved habitat for fish and macroinvertebrates.